Electrical discharge apparatus and process of preparing and using the same



Oct 20,1925. 1,558,436

I. LANGMUIR ELECTRICAL DISCHARGE APPARATUS AND PROCESS OF PREPARING AND-USING 'THE SAIE Original Filed 001:. 16, 1915 Witnesses 40 lhVcntor Irving Langmuir fill; 4 WQ:

His oqttomeg ing and Patented "Oct. 1925.

' um. m

mail-Em OFFICE.

: column, a conroaa'rron or new YORK. I

, mn. Discus-acaarraaaros AND 'rnocn'ss sum.

a plication and me. ia, 101:, Serial no. 795,010. Renewed larch 14, 1916. sermino. 84,242.

To all whom it may concern: h

Be it known that I, IRVING LANG Um, a citizen of the United .States, residrn at Schenectady, county of Schenectady, otNew -York, have invented certain new and useful Improvements in Electrical- Discharge A paratusand Processes of Prepar- V sing the Same, of which the fo1- lowing is a specification.

The present invention relates toelectrical vacuum dischar e devices, and it comprises devices in whio the electrical current. is carried by negative charges called electrons,

, emanating from the cathode, independently of gaseous ionization such as occu'rring,'lor example, in the ordinary Roentgen tube.

My piesent invention comprises improvements in electron-discharge apparatus which make possible a high load'capacity'and op. eration with the highest voltages but the invention is also applicable and. useful for moderate loads and moderate voltages. The

novel featuresof my invention will be pointed out with greater particularity in the appended claims.

Figs. 1 and 2 of the accompanyin draw ings, Fig. j2'being a partial view, ilustrate two types of discharge devices embodying my invention; Fig. 3' is a fragmental view showing-a cathode construction, and Figs.

4 and 5 are diagrams of electrical systems illustrating certain applications of my electron discharge tubes, o

In order to distinguish electron discharge devices made in accordance with my inven tion from the prior art, I will explain briefly the character of a ure electron discharge as distinguished through ionized gas'. Ina Geissler tube,.and in a Roentgen or Crookes tube the conduction of current is accompanied by and depends upon gas ionization. Without a certain minimum amount of gas a Roentgen' X -r'ay tube ceases to operate and asthis minimum is a proache'd the resistance the tube steadi y increases. I

The passage of an electric current across a tube ordinarily involves the movement of negative charges called electrons which,

under the influence of the impressed voltage,

pass from the cathode to the anode through the va'cuous space. "If these electrons when moving above a certain velocity collide with g s m le ule t y t n o ionizethe mol tate mm a discharge cules, splitting them up into electrons and" larger and'more slowly moving ions. Under these circumstances the phenomena of conduction across the. tubes are the result of the action and interaction of the electrons and the ions; these phenomena are in general curs at definitely determinable voltages,

or ranranme m Usrne m positive ions also causes heating 7 these voltages being known as the ionization voltages. different gases. In the-case of gases such as nitrogen, hydrogen, oxygen, argon,

helium and neon, they are of the order of magnitude of fifteen lZOtWGIltY-fiVG volts.

The phenomena above described as being characteristic ofdevices involving gas ionization are taken advantage ofin an incandescent cathode device with three electrodes been used asa receiver for raidio-telegraphy and depends in its operation upon the rapid change of the discharge current when gas ionization begins. This point depends upon ental conditions which cause various acci such rregularities in the operation of ya.-

rious devices apparently identical that sometimes'only one of a considerable number canbe used. Ordinaril the gas ionization in the audion begins -to' e important somewhere These voltages are differentknown as the Audion, This device has between 20 and 30vo1ts. Another discharge 1 device previously used to some extent was theFlemin'g valve; This was a two-electrode tube'which, so far as I am aware, was

always used at voltages Well below the voltages at which positive ionization by collision occurs. It was not evacuated in such a manner as to permit it to be usedat voltages materially above thes ionization voltages without manifesting substantial positive -ionization efiects. No prior hot cathode de vices are known to me operating with currents as great as about 5 milliamperes with voltages as high as about 200 volts; indeed no prior discharge devices are known to me operating in a practically usable manner and without substantial-positive ionization In devices made 1n accordance with my invention gas ionization is either entirely absent or is negligible and a discharge takes place which is distinct in its characteristics from the described discharge taking place in an ionized as. The cathode is not heated by the disc arge itself. Blue glow, glass fluorescence and in fact all rea ily visible indications of a discharge are ordinarily absent. In most devices of simple'construction which embody my invention, the disch e current passing through a given space with the cathode at a sufficiently high temperature with respect to the voltages employed, varies directly with the 3/2 power of the impressed voltages. This 3/2 power law can be readily derived mathematically for a tube in which there is substantially no positive ionization on-the assumption that the whole surface of the cathode is at a uniform potential, that the electrons escape from the cathode with negligible velocities and that the walls of the tube do notcarry appreciable electric charges.

In most simple devices embodying my in-.

vention, these conditions are so well fulfilled that the current does vary in proportion to the 3/2 power of the voltage over wide ranges of voltage above the ionizing voltages. This means that if the logarithm of the current is plotted against the logarithm of the voltage, the resulting plotv is a straight line whose slope is 3/2. Or-,,in many cases it is more convenient to make use of the equivalent relation, that the 2/3 power of the current plotted as ordinates against the anode voltages as abscissa gives a straight line.

In devices in which there is substantial positive ionization, onthe other hand, even when the pressures of gas are so low that only very small currents could be carried by positive ions, the currents begin to increase with voltage more rapidly than accordingto the 3/2 power lawas soon as the anode voltage materially exceeds the ionizing potential of the gas.

In devices embodying my invention which have more than two electrodes, or with special constructions. as where the cathode is a filament, so long that it cannot be considered an equi-potential surface, the 3/2 power law may be more or less masked. However, the efiects thus introduced will be readil understood by those skilled in the art, an appropriate methods of identifying the pure electron discharge can easily be found corre sponding to the special construction. For example, when such tubes have more than two electrodes and the temperature of the cathode is sufliciently high with respectto the voltages employed, the discharge will voltage of the discharge.

usually be characterized by a linear relation between the 2/3 power of the total electron current from the cathode and the voltage applied to any other electrode, the remain,- ing electrodes being kept at constant potential. Another .test that can often be made with a three electrode tube is to connect the grid directly to the anode or to the negative end of the cathode, and observe whether the current varies as the .8/2 power of the voltage.

If for a given cathode temperature the voltage is sufliciently high to cause all of the electrons emitted or liberated at the cathode to be drawn away, then a further increase U in voltage produces substantially no ch in the current. The current thus determined is called the saturation current, and the range of operation in which the current is substantially independent of the volt approaches this condition may be call the saturation range or more briefly designated merely as saturation. If for a given cathode temperature the voltage is not high enough to cause all of the electrons which are emitted or liberated at the cathode to be drawn away, the operation occurs in a range below the saturation range. Operation in this range may be spoken ofas operation below saturation.

A change in the temperature of the cathode in a hot cathode device embodying my invention will produce no change in the discharge when the operation is below saturatlon, even though the ionization voltage is materially exceeded. That is, the currentvoltage curve is not changed by a ch in the cathode temperature under suc conditions.

The discharge in devices embodying myinvention is practically independent of the pressur when the pressure is below a certain value which depends upon the size and shape of the device and upon the current and As distinguished from discharges in they presence of positive ionization. the pure electron discharge is characterized by regularity and reproducibility with given conditions. In a device in which the coduction of current 1s purely electronic. and the elect of III! positiv ions is negligible, the conduction of currentis governed, over a. certain range, on the one hand by the effect of the imp voltage, which tends to propel the electrons across the vacuous space, and on the other hand by the mutual propulsion of the electrons in the space, which tends'to limit 'or inhibit the current. This last mentioned phenomenon, the current effect of the electric field of the electrons on each other, termed the space charge efiect, is di and analyzed by me in a pa r read before the Physical Society on .Octo r 18, 1913, which was abstracted in the Physilll Zeitschrii't for April 1, and May 15, 1914. It

is the basisflof the 3/2power law referred to herein. p

The geometric proportions of the device also affect the amount of current which will pass with a given voltage, but as these conditions remain fixed for a given device they maybe represented by a constant in an equation expressing the relatlon between the current and the voltage.

'As stated above, the current (I) in the particular device described herein, when operatingbelow saturation, will vary with the 3/2 power of the voltage (V), the equation being:

'I='aV/,- (a being a constant) As is well known, if we roduce a logarithmic graph of any equation in which one variable of the equation varies as a power ofthe other variable; as for example, an equation of the general form g m, (asby lotting logarithms of a as abscissae and lbgarithms of y asordinates) we find that this graph is a straight line. Hence the re- 30 lation between current and voltage in a de-' vice operating below saturation and by pure electronic conduction independent of gas ionization may be expressed by the state-- ment that when with a suflicient electron emission the logarithms of the current values transmitted between cathode and anode are plotted as ordinates against the logarithms of the respective voltages impressed between cathode and anode as abscissae,,theslope of the line obtained does not ordinarily increase" regularities will be more manifest when observed as deviations from a straight line blue glow or the like. At saturation on the other hand, the discharge is ordinarily much less sensitive. and in fact the discharge may actually exhibit maked blue glow effects along with a flat or straight saturation curve.

Devices made in accordance with my invention may be used for various techmcal purposes, such as relaying and detecting currents, producing oscillations and rectifying alternating currents, and such devices may be made-which will operate without substantial positive ionization at voltages far abovethc ionization voltages with currents thousands of times greater than the currents at which the devices of the prior art were operable without substantial positive ionization. Devices made and operated in accordance with my invention arecapable of transmitting currents materially, exceeding one-tenthof a milli ampere without causing positive ionization to take any essential part in the operation of the device, though the voltage is materially above the ionization voltages.

Before describing the method of preparing my new type of apparatus, I will describe the structure of the apparatus illustrated by Figs. 1 to 3.

As shown in Fig. '1 the various parts of increasmg g Values V 3 Worklng the apparatus may be mounted in a tube. or

range of voltages extending materially tllXWG the ionization "oltages.

A substantial amountof positive ionization ordinarily causes the logarithmic plot of the current with respect to the voltage to bend upwardly and away from the 3/2 power line when the ionizing voltage is materially exceeded. The absence of a bend in the logarithmic plot at voltages somewhat above the ionization voltage is ordinarily a reliable indication that the tube is a pure electron discharge tube, though saturation complete or partial at voltages somewhat greater than theionization voltages may prevent such a bend in the plot of an ionizing tube. v

As above indicated, one of the indications of positive ionization is the occurrence of erratic readings in measuring devices connected in circuit with an electron discharge device under observation. Such erratic read:

.ings, of course, will produce a sudden change or discontinuity in the logarithmic graph PM as New an re s.

The cathode shown in Fig. 2 consists of a V-shaped conductor. Either form may be used, the particular -form of cathode being ordinarily determined by convenience of construction. Preferably the cathode conductor is held taut'by a spring 7 to avoid contact of the cathode conductor with the grid by sagging when the metal is expanded at a high temperature. The filament 3 is mounted between two oppositely disposed supports, 9, 9, .in thiscase constituting a closed loop, which may consist of insulating material, such as glass or quartz, butin some cases may'to advantage consist of metal Upon this frame-work is wound a dischargevarying conductor 10, ordinarily called a grid. The turns of the wire are closely adjacent to each other and are also very closely adjacent to but are out of contact with the incandescent cathode. 'By means of thi.

grid potential may be applied to exert a 1 as consisting of a wire strung in a zig-zag manner over hooks 13 upon fork-shaped supports 14 and 15, but it is not necessary that it should assume this particular form. Both anode and grid preferably consist of tun n, but other refractory metals may be I use By constituting the anode a continuous conductor it can be conveniently heated by passage of current during evacuatlon oi the device and for this purpose 18 attached to leadin -in conductors 16 and 17 The grid is in icated in Fig. 1 as being attached to leading-in conductors 18 and 19 atflpposite ends, although but one terminal is ordinarily necessary.

In some cases it is desirable to use a plateshaped anode; Fig. 2 illustrates such an arrangement suitable particularly for rectifying alternating current. The tube itself and other extraneous parts have not been shown in Fig. 2, as they are similar to Fig. 1. The cathode construction has already been referred to and the anodes 20 and 21 also preferably consist of tungsten and may be connected electrically with each other. Current connections are made by conductors 22, 23. the supports 24, 25 being merely indicated. It will be noted that both in Flgure 1 and Figure 2 the electrons are afforded a short and direct path from the cathode to the anode and that this path is so related to the position of the walls of the tube as to minimize the tendency for electrons to pass to the walls of the'tube. In such a tube electron bombardment of the walls of the tubr is avoided, together with the heating of such walls and the secondary emission of elechaust are used. The evacuation of the tube the heating may take place by passing an electrical current through the wire 12. The heating, especially of solid anodes such as shown in Figure 2, may take place in a suitable vacuum furnace, the temperature prefcrably' being raised to- 2,500 C. or even higher. Bombardment is a very effective means of removing occluded gas from anodes.

The bombardment is carried out when the evacuation has proceeded to a high degree by applying a potential between the cathode 3 and the anode 12, Fig. 1, the value of which depends upon the character of the device. Care should be taken to use a voltage below that at which a blue glow appears as this indicates harmful gas ionization, and as already pointed out, sputtering and disintegration-of the cathode accompanies or closely follows the blue glow phenomenon. The pump should be constantly operated to remove the After the removal of the as thus riven out the volt age impressed tween the cathode and the anode, or'anodes as the case may be, is increased thereby driving out more gas. This process is continued step by ste with a progressively higher voltage, the a] voltage depending upon the character of the apparatus. In most cases the final voltage should be materially higher than the voltage at which the device is to be used in actual service. However, in the case of devices that use exceedingly high voltages, such as 50,000 volts or even higher, substantially all the gas may be removed from the anode without resorting to voltages higher than the normal operating volta e. In the case of a plate-shaped anode w ich cannot be readily heated by passage of current, the discharge voltage may be chosen great enough to convey suflicient energy to the anode to raise its temperature to redness or even higher, when the device is to be used with a discharge current adapted to heat the anodes.

After the metal has been freed from occluded gas reabsorption of gas will not readily take place even though it is exposed to the air or other gases. For example, anodes thus treated may be removed to other apparatus which then may be evacguano uated with less electron bombardment of the anode or anodes.

The evacuation of the device should be preferably carried to a pressure as low as a few hundredths of a micron, or even lower, but no definite limits can be assigned. The residual'gas ressure should be below the value at whic ionization by collision will take place at the given working volta e and current, with its. accompanying plienomena of blue low, disintegration of the cathode, and so orth. \Vhen the cathode and anode are located in close proximity and the discharge confined to the region between thev same, the ermissible pressure is higher than when tie cathode and anode are at some distance. It is also true that when the anode has been carefully freed from gas, residual free gas, even if present in a suflicient amount to cause some gas ionization when the apparatus is first started, does little harm, as it is quickly removed by the gas clean-up effect when the device is operated.

Electron discharge apparatus thus provi-ded with a gas-free pretreated anode or anodes, may be constructed to handle cur rents at a very high voltage by proper mechanical design of the parts subjected to static strains, suitable proportioning of the parts and so forth as described, for example, in my ap lication Serial No. 795 609 filed concurrent y herewith upon which latent 1,273,783 was granted on uly 23, 1918.

The asymmetric conductivity existing between the heated and unheated electrodes of adevice of the character described may .be utilized for various technical purposes. Reference has'already been made to the rectification of current. As shown in Fig.

4 an electron discharge tube may be used 4 the grid 7 and heated cathode 0 of an electron discharge tube 26 are connected respectively to the terminals of the secondar-y of a transformer 27, the primary of which is included in the antenna circuit 28. The antenna is grounded through a condenser 29 in the usual manner. The cathode 0 is heated by a local source of energy, as batteryjb. A battery 30 in the grid circuit 31 has its negative terminal connected to the grid g. A condenser 32 shunts the secondary of the loosely coupled transformer 27. The inductance of the transformer and the capacity of the condenser are adjusted to make the receiving circuit resonant to the frequency ofth'e oscillations to be received. The oscillations set up by the incoming signals are superimposed upon the negative grid potential and causes a variation of current transmitted between cathode c and anode a by a local source of energy such as a battery 33 included in the local or late circuit 34, 35, of the dischar e tube. is circuit is connected to an o 1- nary telephone receiver 36, preferablyshunted by means of a condenser 37, whereby the signals are detected.

Fig. 5 illustrates how an electron discharge tube may be used in a system for producing alternating current from direct current. The anode a and cathode a are connected respectively to conductors 38, 39, one of which includes a local source of energy, such as a battery 40. The terminals of these conductors are connected to an inductive coil 41. The cathode and grid 9 are also connected respectively by conductors 39 and 42 to a second inductive coil 43 wlnch may be in a variable inductive relation to the coil 41. As soon as a. flow of current starts in the plate circuit 38, 39, current is induced in the coil 43 of the grid circuit 39, 42. When by reason of this current the grid becomes negatively electrified, the flow of current in the plate circuit is reduced, and as the plate current decreases the grid electrification changes to positive, which again allows the current in the plate circuit to increase. These changes take place with a frequency depending on the electrical characteristics of the circuits. Across the grid circuit39, 42, of the discharge tube, in some cases is connected a condenser 44, the capacity of which may be varied to control the frequency of the oscillations set up by the system. The oscillations may be transformed to higher or lower voltage by a transformer coil 45 to the terminals of which are connected transmitting conductors 46, 47. The system shown in Fig. 5 is described and claimed in a copending application, SerialNo. 797,- 987, filed October 29, 1913.

Residual gasdeft in a tube when it is sealed off or occluded gas driven off from the inner wall of the tube, or from the electrodes, during the use of the tubes, varies in pressure from time to time according to the conditions of operation of the tube and may produce irregularities in the discharge when operating in the saturation region as well as when operating below saturation. The irregularities below saturation are due mainly to the disturbing effect of the resulting positive ions upon the space charge. The irregularities in the saturation region are due to changes in the rate of emission or liberation of electrons at the cathode. It is obvious that the advantages of stable and reproducible operation and freedom from destructive bombardment of the oathode by positive ions, which advantages are severally or collectively tobe secured by the means hereinabove described, are not lim ited to operation below saturation but are also important in operation inthe saturation region;

The positive ionization herein referred to is that 'tive ionization which occurs as the ram t of collisions between electrons and gas molecules in the s ace between the eleccure "by Letters Patent. of the United States, is:-v

1. A discharge tube havin electrodes at least one of which is adapte to emit electrons, the as content or residue of said tube and the re ation of the parts of the tube being such that the tube is capableof bein so operated in a range below saturation an materially above ionization voltages that the. governing or limiting action on the space current due to the electric field of said electrons is substantially unafiected by positive ionization and by secondary electron emission from the walls of the tube.

2. A discharge tube having a cathode adapted to emit electrons and an anode adapted to receive said emitted electrons, the tube walls being fashioned or shaped to permit the direct passage of a useful proportion of said electrons from cathode to anode, the gas content or residue of said tube and the relation of the parts of the tube being such that the tube is capable of being so operated in a range below saturation and materially above ionization voltages that the s ace current is governed or limited by the electric field of said electrons substantially unaffected by positive ionization.

3. A discharge tube having electrodes at i least one of which is adapted to emit electrons, the gas content or residue of said tube and the relation of the parts of the tube being such that the tube is capable of being so operated in a range below saturation and materially above ionization voltages that in that ran e the space current is governed by the com ined effect of the electr c field of said electrons and the potentials ap lied to said electrodes, the governin or imiting of the current being substantia ly unaffected by positive ionization and by secondary electron emission from the walls of the tube.

4. A discharge device comprising a tube andelectrodes therein one of which is adapted to emit electrons, the degree of evacuation and the relation of the parts of the device being such that the device is capable of being so operated, when voltages materially higher than ionization voltages are, impressed upon electrodes of the device and when the electron emission has any value such that the space current is below the saturation region at such voltages, that the slope-of the line obtained by plotting the logarithms of values of said current as ordinates against the 10 rithms of the corresponding values of sai impressed voltages uses as abscissa: showsno increase for increasin volta values.

5. dischar device comprising a tube. and electrodes t erein one of which 18 ads ted to emit electrons, the degree of evacuation and the relation of the parts of the device being such that the device is capable of being so 0 rated, when voltages materially higher t an ionization volta es are impressed on electrodes of the device and when the electron emission has any value such that the space current is below the saturatlon rggion at such voltages, that the line obtain by plotting the logarithms of any values of said current below the saturation region as ordinates against the 10 arithms of the corresponding values of sai impressed voltages as abscissa is straight and continuous.

6. A discharge tube havin least one of which is adapted trons, the gas content or residue of said tube and the relation of the parts of the tube being such that the tube is capable of being so operated, when voltages materially high-1 er t an ionization voltages are impressed on electrodes of the tube and when the electron emission has any value such that the space current is below the saturation region at such volta es, that said current varies as the three ha ves power of said impressed voltages. V

7. A discharge device com rising a tube and electrodes therein one 0? which is an electron emittin cathode, the degree of evacuation of sai device and the relation of the parts of the device being such that the device is capable of being so operated, when voltages materially higher than ionization voltages are impressed on electrodes of the device and when the electron emission is such that the space current is below the saturation re ion at such voltages, that said current is su stantially independent of the cathode temperature and unaffected by secondary electron emission from the walls of the tu 8. A discharge tube having electrodes at least one of which is adapted to emit electrons, the as content or residue of said tube and the re ation of the parts of the tube being such that the tube is capable of bei so operated in a range below saturation an materially above ionization voltages that the space current is governed or limited by the combined effect of the electric field 01 said electrons and the potentials applied to said electrodes, substantially unaffected b positive ionization, the heating efiect in t e tube due to said currentr occurring substantially only at one or more of said electrodes.

9. A discharge tube having a cathode adapted to emit-electrons, an anode adapted to receive electrons and tube walls fashioned electrodes at to emit elecof a useful proportion of said electrons from cathode to anode, the content or residue of said tube and the re ation of the parts of the tube being such that the tube is capable of operation with stable and reproducible results substantially unaffected by positive ionization, with currents of at least 5 milliai'nperes and with voltages of at least 200 volts.

10. An electrical discharge device comprising a gas-tight envelope, an electronemitting cathode, a cooperating anode, and

a dischar -vary1ng conductor, the s ace in said enve ope being evacuated to be ow the pressure at which eleterious gas ionization takes place, constituting a device in which the rcurrent passed when operated below saturation and over a workin range of voltage materiall above the ionization voltages 18 controlle by space charge substantially unaffected by positive ionization.

11. A high vacuum electron discharge device comprising an envelo e, an incandescent cathode, and an ano e, the space in said envelope being evacuated to such degree that the passage of current produces no appreciable ositive ionization when the impressed vo tags is as high as 200 volts 12. An electrical discharge device, comprising a gas-tight envelope, an electron emitting cathode, ,an anode deprived of ionizable gas and a discharge controlling conductor, the space in the envelope being evacuated to a pressure not substantially in' excess of a few hundred thousandths of a millimeter of mercury, said device being characterized by the fact that when operated below saturation and materially above the ionization voltages, the current is controlled by space charge substantially unaffected by positive ionization.

13. An electrical discharge device comprising a gas-tight envelope, an electron emitting cathode, a cooperating anode, the space and materials in said envelope being sufficiently free of gas so that substantially no positive ionization occurs when the impressed voltage is as high as 60 volts, and the current over a working range of voltage up to 60 volts varies with the 3/2 power of .the impressed voltage.

. 14. 'An electrical discharge device comprising a gas-tight envelope, a cathode ,adapted to be heated to incandescence, an anode from which substantially no ionizable 66 electrodes so positioned as to substantially avoid secondary electron emission from the wall of the envelope, the space .in said onvelope being evacuated to. a pressure not in substantial excess of a few hundred thousandths of a millimeter of mercury.

15. A device comprising a gas-tight enworking range below saturation varies with the 3/2 power of the voltage.

16. An electrical discharge device comprising a sealed envelope, an incandescent cathode, and a tungsten anode, said anode deprived of ionizable gas disengageable by electron bombardment, and the space in said envelope being evacuated to a sufficiently low pressure so that current flow produces substantially no phenomena of positive ionization when the impressed voltage is as high as volts and the current is as large as 1 milliampere, and the energy of the discharge is delivered mainly upon said anode.

17. An electron discharge apparatus comprising an envelope, an electron emitting cathode, and an anode, said anode being free of gas disengageable by electron bombardment and said envelope being sufficiently free of gas, so that conduction of current can take place in the evacuated space inde ampere, and with the energyof 'tilie (iischarge delivered mainly at said anode. I 18. An electrical discharge device comprising a sealed envelope, acathode, means for producing emission of electrons at said cathode independently of the operating voltage, an anode, and discharge varying means independent of the cathode and anode, said device being freed from gas to such extent that the same is operable to transmitcurrent at an impressed voltage at least as high as about 200 volts without evidences of substantial positive ionization.

19. An electrical discharge device comprising a sealed envelope,'an incandescent cathode, an anode and dischar e-varying. means independent of the catho e and anode, the gas residues in said device being so small that the conduction of current is stable and reproducible over. a range of voltage materially .above the. ionization voltages with currents in excess of one milliampere and with the energy of the discharge delivered mainly upon electrodes.

Anelectrical device comprising the combination of a sealed evacuated envelope, a cathode adapted 'to be independently heated, and an'anode within said envelope,

an external circuit connected to said electrodes, and a source of electro-motive force applied to said circuit, the degree of vacuity and the electron emission of the cathode being so related to the potential of said source a that. the flow of current over a range of voltage r'nfiteriall above the ionization volt- .is governed; electric field of the a efie ct iiithe vacuousspaeeand the-potenti l aTpplied toSl i, m eaoperaftively indepen ent of ionisation.

21. Apparat ,controlli an electric current comp fif -vacuum to an anode and an electron emitting cathode in the circuit'of said competing! wit in said tube, the. degree of evacuatioii'fof t e tube and the relation of its artibeing such that for voltages materia y above ionization voltage the current is verned or limited by the electric field o the electrons in said tube substantially unafl'ected by positive' ionization, and-a third electrode in said tube by i which an auxiliary controlling electromotive force may be superposed to modify the ef- :fect of said electric field and control said currentin a stable and reproducible manner. 22. The method of controlling an electric current, in one circuit by an electromotive tor-(e in another circuit which consis'tsin causing said current at voltages materially above Ionization voltages to pass as a discharge across avacnous space between an electron emitting cathode and an anode,

maintaining a' high vacuum in said space, governin or limiting the current by a space charge e out in said space substantially unaffected by positive ionization, and superimposing the eli'ect of said electromotive force on said space charge efiect to control said current in astable and reproducible manner.

23. A discharge device comprising a tube and electrodes. therein, one of which is a cathode, the discharge passing in the main directly between electrodes, the degree of evacuation and the relation of the parts of the device being such that the device is caelectrons thereby, the dischar e passing directly between electrodes, tie degree of evacuation and the relation of the parts of the device being such that the device is capable of being so operated below saturation and at volta materially higher than the ionization vo tags, that the plot of the current against the voltage is not changed with changes in the temperature of the cathode.

25. A discharge device compnsmg a therein a cathodesealedofl envelope hav' ,findently of the 6 ,ner. with currents of more than one milli- 15 ampere at vol materially 11' her the ionization v0 ta and with energy, of the discharge delivered mainly at an electrode (X elgctriodes. d

26. isc large evice com rmng' a 00 sealed ofl' envelope and electrode: thbrein, the envelope being shaped and the electrode! located so that the energy of the is delivered mainly upon one or more of electrodes, the inner wall.of the envelope II and electrodes being so free from occluded gas and the pressure in the-tube sum cientl low, with res t to the aclng or the ectrodcs and t e ener o the discharge, so that the device is capable of O0 passln a sustained dischar of one tenth of a milliampere at fort vo ts, without developing any substantia positive ionization effects.

27. A discharge device comprising a ll sealed oil envelope and electrodes therein, one of which is a cathode adapted to be, heated independently of the discharge and to emit electrons thereby, the inner wall of the envelope and the electrodes being so free from occluded gas that the device is 68-, pable of passing a sustained discharge of one milliam ere at fifty volts with the energy of the disc large delivered mainl at an electrode or at electrodes without iberating any substantial amount of gas into the space within the envelope.

28. A discharge device comprising sealed-oil envelope and electrodes therein, one of which is a cathode ada ted to be 110 heated independently of the disc arge and to emit electrons thereby, the inner wall of the envelope and the electrodes being so free from occluded gas that the device is capable of passing a sustained discharge of two milliam res at one hundred volts with the energy 0 the discharge delivered mainly at an electrode or at electrodes without libcrating any substantial amount of ga s intothe space withinthe envelope.

29. An electrical discharge device comprising a gas-tight envelope, a cathode adapted to be heated to incandescence, an anode from which substantially no ionizable gas can be evolved at operating voltagesv up to forty volts with currents up to one'tenth milhampene, the envelo so shaped and the electrodes so positio ed as to substantiallyavoid secondary electron emission from the wall of the envelope, the space in said entrons thereby,

unease velope being evacuated to a ressure not insubstantial excess of a few undred thousandths of a millimeter of mercury.

, 30. In the. process of produclng a discharge device, removing the occluded gas from the interior surface of the envelope thereof and from the electrodes to such an extent that the finished sealed-E device will iii low saturation in a stable and reproducible operate, without liberating any substantial amount of gas into the space within the envelope, at voltages materially above the ionization voltage with currents greater than one milliampere and with substantially all the ener of the discharge delivered to an ano e or anodes.

31. In the process of producing a hot cathode discharge device, treating the interior surface of the envelope and t e operating parts to liberate therefrom occluded s, and removin from the envelope gas iberated by sai treatment and free gas originall contained therein, continuing these operations until the occluded and original free is so thoroughly removed as to enable finished sealed-ofl device to operate bemanner at avoltage above fifty volts and with a current greater than one milliampere and with the energy of the discharge delivered mainly at one or more anodes.

32. The process of producing a discharge device which consists in treating the envelope and enclosed parts thereof to liberate gas therefrom and removing from the en- .velope gas which is thereby liberated and free gas originally contained in the en-% velo the treatment bein sufliciently powerfu and bein sufficient y prolonged and the removal 0 the liberated and original free gas from the envelope being sufliciently thorough, so that the finished sealed-off device is capable of sustained o ration substantially without positive ionization at voltages as high as one hundred volts with currents as great as one milliampere and with substantially the entire energy of the dischar delivered upon the anode or anodes of the evice.

In witness whereof, I have hereunto set my hand this 15th day of October 1913.

nwmo LANGMUIB- 

